Quaternary ammonium catalyst system for the polymerization of 2-pyrrolidone

ABSTRACT

The process of making a catalyst for the polymerization of 2-pyrrolidone by contacting an alkali metal pyrrolidonate, a quaternary ammonium halide and carbon dioxide in a mol ratio of about 1:0.1-2:0.1-0.5. The alkali metal pyrrolidonate may be prepared by reacting an alkali metal hydroxide with 2-pyrrolidone. The polymerization of 2-pyrrolidone in the presence of this catalyst system produces poly-2-pyrrolidone of high molecular weight.

This is a division of application Ser. No. 687,968, filed May 19, 1978,now U.S. Pat. No. 4,098,774.

BACKGROUND OF THE INVENTION

Poly-2-pyrrolidone is produced by the alkaline-catalyzed polymerizationof 2-pyrrolidone. The catalyst system may comprise a partiallycarbonated pyrrolidonate salt made, for example, by reacting an alkalimetal hydroxide with 2-pyrrolidone, or by reacting a quaternary ammoniumhydroxide with 2-pyrrolidone, dehydrating, and contacting the productwith carbon dioxide (U.S. Pat. No. 3,721,652). Japanese Patent No.47-26195 discloses a process for making a catalyst by reacting anon-water-forming alkali metal compound with 2-pyrrolidone andcontacting the product with a quanternary ammonium halide underanhydrous conditions. In U.S. Pat. No. 3,835,100, the catalyst obtainedby reacting an alkali metal alkoxide with a quaternary ammonium halideand contacting the product, ammonium alkoxide, with 2-pyrrolidone, alsoavoids the production of water. While both of the latter processes areanhydrous, they do not produce poly-2-pyrrolidone of very high molecularweight in ordinary reaction times. For many processes, it isadvantageous to be able to rapidly produce poly-2-pyrrolidone havinghigh molecular weight, e.g. in excess of 500,000 in good yield.

BRIEF SUMMARY OF THE INVENTION

A catalyst capable of producing a high-molecular-weightpoly-2-pyrrolidone is made by contacting an alkali metal pyrrolidonate,certain quaternary ammonium halides and carbon dioxide the mol ratio of1:0.1-2:0.1-0.5.

DESCRIPTION OF PREFERRED EMBODIMENTS

While poly-2-pyrrolidone of 300,000 weight average molecular weight isproducible over a polymerization period of less than 24 hours by using apartially carbonated potassium pyrrolidonate catalyst, the catalyst ofthe present invention is capable of producing poly-2-pyrrolidone havinga weight average molecular weight in excess of 1,000,000 under the sameconditions. The present catalyst also achieves high yields and highconversion rates without diminution of molecular weight. The catalystdoes not require an anhydrous source of alkali metal pyrrolidonate. Thepyrrolidonate may be made by contacting 2-pyrrolidone with thehydroxide, rather than by contacting it with an alkali metal or alkalimetal alkoxide.

CATALYST SYSTEM

In the process of the present invention a catalyst for thepolymerization of 2-pyrrolidone is made by contacting an alkali metalpyrrolidonate, certain quaternary ammonium halides and carbon dioxide inmol ratio of about 1:0.1-2:0.1-0.5, preferably in mol ratio of about1:0.2-1.5:0.1-0.5, and most preferably in a mol ratio of about 1:1:0.3.

The reactants, the pyrrolidonate, the halide and carbon dioxide, may becontacted in any order beginning with the pyrrolidonate as one of thecomponents. It is preferred, but not necessary, to add the quaternaryammonium halide to the previously carbonated pyrrolidonate salt. In apreferred embodiment, the catalyst of the present invention is formed ina solution of 2-pyrrolidone. An alkali metal hydroxide is added to anexcess of 2-pyrrolidone, with which it reacts to produce a solution ofthe alkali metal pyrrolidonate and water in 2-pyrrolidone. The solutionis dehydrated until it contains less than about 0.1-0.2 weight percentwater. Then carbon dioxide is added in the required mol ratio to thepyrrolidonate in the solution at a temperature of about 25°-30° C. Thequaternary ammonium halide is also added in the required mol ratio tothe pyrrolidonate at about the same temperature.

Another method for preparing the catalyst systems of this inventioninvolves the in situ preparation of tetraalkyl ammonium halide by thereaction of trialkylamine with an alkyl halide. For example, a portionof the 2-pyrrolidone monomer may be used as a solvent in which the abovereaction is carried out. The reaction involves dissolving thetrialkylamine in this pyrrolidone and then adding the alkyl halide whileat the same time maintaining the temperature within the range of about10 to 50° C. When the reaction is completed, the resulting solution isreacted with alkali metal pyrrolidonate and carbon dioxide as byaddition to a pyrrolidone solution in which the carboxylated alkalimetal salt has already been prepared by the usual procedures.

The quaternary ammonium halide is preferably a tetraalkyl ammoniumhalide, although alkylaryl ammonium halides, such as phenyl trimethylammonium halide and tolyl triethyl ammonium halide, are included withinthe scope of the ammonium halides of this invention. The tetraalkylammonium halide is preferably a tetra (C₁ -C₆) alkyl ammonium halide,and most preferably a tetra (C₁ -C₃) alkyl ammonium halide.Representative alkyl groups include methyl, ethyl, propyl, isopropyl,butyl, isobutyl, t-butyl, hexyl, etc. The ammonium halide is preferablya chloride, bromide or iodide or more preferably a chloride or bromide,most preferably a chloride. The ammonium halide may be used as acombination of species, e.g., as a mixture of tetramethyl ammoniumchloride and tetraethyl ammonium bromide. The ammonium halide should besubstantially soluble under the alkaline conditions of catalyst systempreparation in order to show an appreciable effect on the polymerizationreaction.

The ammonium halides finding use within the scope of this inventioninclude compounds such as R¹ R² R³ (φCH₂) NX wherein φ represents aphenyl and R¹, R² and R³ may be the same or different alkyl groups orother aralkyl groups, and X is a halide. Consequently, ammonium halide,as used herein encompasses the aralkyl ammonium halides. These aralkylgroups will normally contain 7-12 carbon atoms e.g. benzyl, phenethyletc.

The alkali metal pyrrolidonate is preferably sodium or potassiumpyrrolidonate. For certain purposes, it may be advantageous tosubstitute for pyrrolidonate in whole or in part an alkali metalcaprolactamate or the alkali metal salt of another low-molecular-weightlactam, but this is normally not preferred to the use of thepyrrolidonate. The alkali metal pyrrolidonate is preferably made bycontacting the alkali metal hydroxide with excess 2-pyrrolidone, butother methods may be chosen, such as by reacting 2-pyrrolidone with analkali metal or an alkali metal alkoxide. While it is preferable tocontact the tetraalkyl ammonium halide, the pyrrolidonate and carbondioxide in a 2-pyrrolidone solution, inert solvents may be used in wholeor in part to replace the 2-pyrrolidone. Sulfur dioxide is believed tobe an inferior substitute for carbon dioxide, but its use is not barredin the practice of the present invention.

In the catalyst system of the present invention, polymerizationinitiators and polymerization accelerators may also be used.Unexpectedly rapid polymerization to poly-2-pyrrolidone ofsatisfactorily high molecular weight is achieved in this catalyst systemby the addition of 0.05-1.5 mol percent of acetic anhydride. Preferably0.05-1.0 and most preferably about 0.05-0.5 mol percent of aceticanhydride is used. Suitable accelerators are also described in U.S. Pat.No. 3,721,652 and include N-acyl lactam, particularly the N-acylpyrrolidones, preferably N-acetyl pyrrolidone and1-(1-pyrrolin-2-yl)-2-pyrrolidone.

POLYMERIZATION CONDITIONS

The polymerization process of this invention is specifically applicableto the polymerization of 2-pyrrolidone to form a polymeric carbonamideof very high molecular weight in a reasonably short polymerization timefor this reaction of 4-24 hours. Weight average molecular weights inexcess of 1,000,000 have been attained. The high-molecular-weightpolymer is capable of being formed into filaments having substantialorientation along the filamentary axis, high tensile strength and otherproperties suitable for making into textiles. It can be made into shapedarticles and film by melt-molding or extrusion.

In order to produce high-quality poly-2-pyrrolidone capable of beingformed into fibers, filaments and yarn of commercial textile quality, itis necessary that the 2-pyrrolidone be of high purity. Depending uponthe process of manufacture, commercially available 2-pyrrolidone maycontain appreciable amounts of various impurities, some of which arebelieved to interfere deleteriously with polymerization. Purification ofthe monomer to polymerization grade is achieved by known purificationtechniques, including distillation.

The process of the present invention is just as applicable to theproduction of polymers of C-alkyl-substituted pyrrolidone, such as4-methyl-2-pyrrolidone and copolymers of 2-pyrrolidone, such as withcaprolactam, as to the production of poly-2-pyrrolidone. Consequently,in general, and unless otherwise indicated, "monomer" denotes2-pyrrolidone, subtituted 2-pyrrolidone, and any compound capable ofcopolymerizing with 2-pyrrolidone under the stated conditions ofalkaline polymerization catalysis.

Preferably the catalyst system comprises about 0.5-30 mol percent ormore of the 2-pyrrolidone-catalyst mixture, based on total2-pyrrolidone, preferably about 5-20 mol percent, and most preferablyabout 10 mol percent catalyst. Total 2-pyrrolidone consists of2-pyrrolidonate catalyst, including alkali metal pyrrolidonate andquaternary ammonium pyrrolidonate, as well as carbonated alkali metalpyrrolidone and carbonated quaternary ammonium pyrrolidonate, and2-pyrrolidone provided as solvent to said catalyst, and any additionalmonomer charged to the mixture for polymerization reaction. Thepolymerization catalyst system is believed to principally comprisequanternary ammonium pyrrolidonate and carbonated quaternary ammoniumpyrrolidonate, but substantial amounts of alkali metal pyrrolidonate andcarbonated alkali metal pyrrolidonate (carboxypyrrolidonate) may also bepresent, depending upon the mol ratios chosen. Alkali metal halide isthought to be present, but it is believed to be inert towards thepolymerization reaction.

In general, 2-pyrrolidone may be polymerized at a temperature from about15° C. to about 100° C., preferably 25° C. to 70° C., and mostpreferably from about 40° C. to about 60° C., under a pressure rangingfrom subatmospheric to superatmospheric, in the presence of the catalystsystem for a period from about 4 to about 100 hours or longer,preferably for about 8 to about 72 hours, and most preferably from about8 to about 48 hours. In continuous operation, polymerization time refersto average residence under polymerization conditions. A small amount ofwater, not exceeding about 0.1-0.2 weight percent, based on total2-pyrrolidone, is permissible in the reaction mixture, but less than 0.1weight percent is preferred.

Preparation of polymers of 2-pyrrolidone, according to the normalprocess of this invention, can be carried out with various amounts ofmonomers, catalyst, inert nonsolvent liquids, initiators and otheradditives-- the amount of each being properly coordinated to produce themost effective polymerization. Although the preferred conditions andamounts of the components in the reaction have been given, it isunderstood that these are not intended to be limitations topolymerization, since it may be possible to achieve substantialpolymerization outside the preferred ranges.

EXEMPLIFICATION EXAMPLE 1

100 g of 2-pyrrolidone (1.175 M) was mixed with 1.55g of 85.5% KOHpellets (0.0236M) to make a 2 mol percent potassium pyrrolidonatesolution which was dehydrated by heating to incipient distillation at 2mm pressure for 11 minutes. To the dehydrated solution was addedsufficient carbon dioxide to make a polymerizate containing 30 mol % CO₂based on potassium. The carbonated 2-pyrrolidone solution was pouredinto 2 bottles, one of which was held at 50° C. for 8 hours, the otherheld at 50° C. for 22 hours. After these time intervals the contents ofthe bottles were chopped, washed with water, dried, weighed andsubjected to viscosity measurement for molecular weight determination asdescribed. The results are presented in Table I.

EXAMPLE 4

Same as Example 1 except for the addition of 2.59g (0.0236M) of tetramethyl ammonium chloride after carbonation by weighing the dried oniumsalt in a dry box and adding same under N₂ at room temperature to thepolymerizate with stirring for 5 minutes. The remaining procedure was asin Example 1.

EXAMPLE 13

100 g (1.175M) of 2-pyrrolidone was mixed with 3.85g of 85.5% KOHpellets (0.0588M) to form a 5 mol percent potassium pyrrolidonatesolution which was dehydrated by heating to incipient distillation at 2mm pressure for 10 minutes. To the dehydrated solution was added 30 mol% carbon dioxide based on potassium. Then 0.12 g of acetic anhydride(0.1 mol percent based on total monomer) was added dropwise to thestirred polymerizate which was polymerized for 8 hours at 50° C. Theproduct was chopped, washed, dried, weighed and subjected to molecularweight determination. The results are given in Table IV.

EXAMPLE 15

Same as Example 13 but 6.44 g (0.0588M) of tetramethyl ammonium chloridewas added after carbonation to make a 5 mol % solution based on totalmonomer. Then 0.12g of acetic anhydride was added. The remainingprocedure was as in Example 13.

The polymerization process of this invention produces a high molecularweight poly-2-pyrrolidone at a high rate of conversion without producingthe unpleasant odors which are sometimes associated with the dehydrationof quaternary ammonium hydroxide-2-pyrrolidone mixtures. The combinationof carbon dioxide polymerization activation and quaternary ammoniumhalide as a source of polymerization catalyst produces extremely highmolecular weight polypyrrolidone. The addition of about one mol percentacetic anhydride has the additional effect of greatly accelerating therate of polymerization.

Table I shows several polymerizations in the presence of potassiumpyrrolidonate and carbon dioxide (Py-K/CO₂) with and without tetramethylammonium chloride. The tetramethyl or tetraethyl ammonium chloride incombination with carbon dioxide and potassium pyrrolidonate are found tobe capable of producing polypyrrolidone of an extremely high weightaverage molecular weight in excess of one million. All molecular weightsare reported as the weight average molecular weight determined from thespecific viscosity of 0.1 gram of polymer/100cc of m-cresol solution at25° C. All reported percentages are mol percent unless otherwiseindicated.

    __________________________________________________________________________    TABLE I                                                                       8 hours.sup.1                                                                       % Py--K/CO.sub.2 2                                                                    % (CH.sub.3).sub.4 NCl                                                                % Conversion                                                                          Mw × 10.sup.-3                            __________________________________________________________________________    Example 1                                                                           2       0       8.5     117                                             Example 2                                                                           2       0       16.3    285                                             Example 3                                                                           10      0       14.4    305                                             Example 4                                                                           2       2       15.0    210                                             Example 5                                                                           5       5       40.0    575                                             Example 6                                                                           10      10      53.9    980                                             22 hours.sup.1                                                                Example 1                                                                           2       0       20.1    220                                             Example 2                                                                           5       0       45.2    380                                             Example 3                                                                           10      0       48.3    500                                             Example 4                                                                           2       2       37.7    330                                             Example 5                                                                           5       5       69.1    1050                                            Example 6                                                                           10      10      59.42   820                                              .sup.1 50° C.                                                          .sup.2 30 mol % CO.sub.2 based on K.                                     

    TABLE II.sup.1                                                                              Mol Ratio                                                             % (CH.sub.3).sub.4 NCl                                                                (CH.sub.3).sub.4 NCl/K                                                                % Conversion                                                                          Mw × 10.sup.-3                            __________________________________________________________________________    Example 2                                                                           0       --      45.2    380                                             Example 7                                                                           1       0.2     62.9    555                                             Example 8                                                                           2       0.4     68.7    635                                             Example 5                                                                           5       1.0     69.1    1050                                            Example 9                                                                           7.7     1.5     69.2    605                                              .sup.1 22 hours, 50° C., 5 mol % Py-K/CO.sub.2 (30 mol% CO.sub.2       based on K)                                                              

    TABLE III                                                                           Carbonated                                                                    Pyrrolidonate,                                                                        Ammonium                                                              5%      Halide, 5%                                                                            % Conversion                                                                          Mw × 10                                   __________________________________________________________________________    Example 1                                                                           Py--K--CO.sub.2.sup.1                                                                 0       45.2    380                                             Example 5                                                                           "       (CH.sub.3).sub.4 NCl                                                                  69.1    1050                                            Example 10                                                                          Py--Na/CO.sub.2.sup.2                                                                 0       34.8    295                                             Example 11                                                                          "       (CH.sub.3).sub.4 NCl                                                                  48.5    380                                             Example 12                                                                          "       (C.sub.2 H.sub.5).sub.4 NCl                                                           67.4    385                                              .sup.1 From KOH, 50° C., 22 hours, 30 mol % CO.sub.2 based on K        .sup.2 From Na-alkoxide, 50° C., 22 hours, 30 mol % CO.sub.2 based     on Na                                                                    

    TABLE IV                                                                            %(CH.sub.3).sub.4 NCl                                                                   %Ac.sub.2 O.sup.1                                                                       %Conversion.sup.2                                   __________________________________________________________________________    Example 2                                                                           0         0         16                                                  Example 13                                                                          0         0.1       47                                                  Example 14                                                                          5         0         40                                                  Example 15                                                                          5         0.1       76                                                  __________________________________________________________________________     .sup.1 Acetic anhydride, mol%                                                 .sup.2 8 hours at 50° C., 5 mol% Py--K/CO.sub. 2 (30 mol % CO.sub.     based on K)                                                              

The examples of Table I show the remarkably high weight averagemolecular weights obtainable from the catalyst system of the presentinvention with good conversions of monomer to poly-2-pyrrolidone inremarkably short times for these molecular weights in this reaction.Percent conversion is calculated as 100× (weight of polymer)/(weight oftotal 2-pyrrolidone) and total 2-pyrrolidone has been definedheretofore.

The examples of Table II show the effect of mol ratio of alkali metal,e.g., potassium hydroxide, to tetralkyl ammonium halide. The highestmolecular weights are believed to be achieved at about equimolar amounts(equivalent amounts) of the alkali metal pyrrolidonate and thetetraalkyl ammonium halide.

Table III shows the effect of an anhydrous source of alkali metal vs. awater-forming source, i.e., alkali metal hydroxide which reacts with2-pyrrolidone to produce water, with and without 5 mol percent of thespecified halide. In general, the hydroxide is a very satisfactorysource of alkali metal for this catalyst system.

Table IV shows the remarkable effect produced on the rate ofpolymerization by the addition of a small amount of acetic anhydride tothis catalyst system. 76% conversion is achievable after only 8 hours at50° C., giving a product having a molecular weight of 175,000.

                  TABLE V                                                         ______________________________________                                        %Ac.sub.2 O.sup.1                                                                          %(CH.sub.3).sub.4 NCl                                                                    %Conversion.sup.4                                                                        M.sub.w × 10.sup.-3                  Example 16.sup.2                                                                      0        0           4.1      35                                      Example 17.sup.3                                                                      0        5          35.4     165                                      Example 18.sup.3                                                                      0.6      5          48.2     150                                      Example 19.sup.3                                                                      1.11     5          75.7      56                                      ______________________________________                                         .sup.1 Mol percent acetic anhydride                                           .sup.2 10 mole percent KOH (K-pyrrolidonate), no CO.sub.2                     .sup.3 5 mol percent, KOH (K-pyrrolidonate), no CO.sub.2                      .sup.4 22 hours, 50° C.                                           

Table V shows the effect of omitting CO₂ from the catalyst system.Molecular weights are found to be lowered. While the addition of aceticanhydride gives high conversion at 22 hours the average molecular weightin the absence of carbon dioxide is still lowered.

                  TABLE VI                                                        ______________________________________                                        Ammonium Salt.sup.1                                                                           %Conversion Mw × 10.sup.-3                              ______________________________________                                        --              32.9        390                                               (CH.sub.3).sub.4 NCl                                                                          69.1        1050                                              (CH.sub.3).sub.4 NBr                                                                          35.0        420                                               (CH.sub.3).sub.4 NI                                                                           33          380                                               (C.sub.2 H.sub.5).sub.4 NCl                                                                   73.2        1025                                              (C.sub.2 H.sub.5).sub.4 NBr                                                                   51.6        610                                               (C.sub.2 H.sub.5).sub.4 NI                                                                    33          390                                               (C.sub.2 H.sub.5).sub.3 (0CH.sub.2)NCl                                                        63.9        880                                               (C.sub.2 H.sub.5).sub.3 (0CH.sub.2)NBr                                                        49.1        510                                               (C.sub.4 H.sub.9).sub.4 NI                                                                    23.9        410                                               (CH.sub.3).sub.3 (CH.sub.2 CH.sub.2 OH)NCl                                                    17.9          95                                              (CH.sub.3).sub.3 HNCl                                                                         0           --                                                H.sub.4 NCl     0           --                                                ______________________________________                                         .sup.1 In mol ratio K/ammonium salt = 1-1.3 5 mol% KOH (K-pyrrolidonate),     1.5 mol % CO.sub.2 based on total 2-pyrrolidone                               .sup.2 22 hours at 50° C.,                                        

Table VI shows the results obtained with a variety of ammonium halidesincluding some remarkably high molecular weights for poly-2-pyrrolidone.

What is claimed is:
 1. The process of making catalyst for thepolymerization of 2-pyrrolidone comprises contacting an alkali metalpyrrolidonate, a tetraalkyl ammonium halide and carbon dioxide in molratio 1:0.1-2:0.1-0.5.
 2. The process of making catalyst for thepolymerization of 2-pyrrolidone comprises contacting an alkali metalpyrrolidonate, a quaternary ammonium halide and carbon dioxide in molratio of about 1:0.2-1.5:0.1-0.5.
 3. The process according to claim 1wherein said tetraalkyl ammonium halide is selected from amongtetramethyl, tetraethyl and tetrapropyl ammonium chlorides or bromides.4. The process according to claim 1 wherein said alkali metalpyrrolidonate is potassium pyrrolidonate.
 5. The process according toclaim 1 wherein said mol ratio is about 1:1:0.3.
 6. The processaccording to claim 1 wherein said tetraalkyl ammonium halide is tetra(C₁ -C₆) alkyl ammonium halide.
 7. The process according to claim 1wherein said alkali metal pyrrolidonate is prepared by contacing analkali metal hydroxide with 2-pyrrolidone.
 8. The process according toclaim 1 wherein said tetraalkyl ammonium halide is a chloride, bromideor iodide.
 9. The process according to claim 1 wherein said tetraalkylammonium halide is a tetra (C₁ -C₃) alkyl ammonium halide.
 10. Theprocess according to claim 1 wherein said tetraalkyl ammonium halide istetramethyl ammonium halide.
 11. The process according to claim 1wherein said tetralkyl ammonium halide is selected from tetramethyl ortetraethyl ammonium halide and said alkali metal pyrrolidonate isprepared by contacting potassium hydroxide or sodium hydroxide with2-pyrrolidone.